Mystery has surrounded the death of the former KGB officer since he died after drinking tea laced with radioactive polonium-210 with two ex colleagues at a London hotel in 2006.

The Daily Telegraph reports that Home Secretary Theresa May will tell Parliament that a public inquiry will take over from the inquest.

A Government spokeswoman said: "An announcement in relation to the death of Alexander Litvinenko is due to be made on Tuesday morning. We will provide no further details until an announcement has been made to the House."